Manufacture of cellulose esters



Patented Oct. 12, 1937 i VUNITED smrs ATENT OFFICE MANUFACTURE OF GELLULOSE ESTER/S John Edward Jones, Spondon, near Derby, England, assignor to Celanese Corporation of America, a corporation of Delaware N Drawing. Application January 3, 1936, Serial No. 57,398. In Great Britain January 16, 1935 Claims. (Cl. 260102) This invention relates to the manufacture and The cellulose ester may be subjected to the statreatment of organic esters of cellulose, and bilizing treatment in any suitable form, but it is particularly to the manufacture of organic esters preferably treated in the form in which it is pre of cellulose of a high degree of stability. cipitated from esteriiication or ripening solutions.

.5 V The esterification of cellulose is usually carried The precipitated cellulose ester may be washed 5 out in the presence of catalysts, of which the prior to the stabilizing treatment and/or may be most common is sulphuric acid. The esters protreated with a substance of weakly alkaline reduced by such processes are, however, in general, action with a view to removing any substantial contaminated with the catalyst, such catalyst beexcess of acid present. Thus where an acid cata- 0 ing present in admixture and/or combination lyst such as sulphuric acid has been employed with the cellulose ester. The removal of such in the esterifying process the excess of such acid catalyst is highly desirable for the production of may be neutralized by the addition of salts such cellulose esters of good stability, and it is thereas the acetates, carbonates or bicarbonates of fore customary to subject the cellulose ester to a sodium, potassium or ammonium. Complete neuprocess generally referred to as stabilization, in tralization of the sulphuric acid is, however, un- 15 which the cellulosic esters are treated with an necessary, and, in fact, the retention of a small agent such as hot water or hot diluteacid, in amount of free sulphuric acid in the material order to remove the catalyst from admixture may facilitate the stabilization. and/or combination therewith. Such stabilizing Any suitable stabilizing liquor may be emg processes are usually carried out with more or ployed in the process of the present invention, less vigorous agitation of the mixture of cellulose e. g. hot water, but preferably acid stabilizing ester and hot aqueous medium. liquors are employed as, for example, hot dilute According to the present invention the stasolutions of acids. Preferably a dilute sulphuric bilization of cellulose esters is effected while acid solution in which the sulphuric acid concen- 5 maintaining the cellulose ester inv a substantially tration is of the order of 0.01 to 0.03% is emstationary state, the stabilizing liquor being ployed, and such as a solution forms a very satispassed continuously through the mass of cellufactory medium for the stabilization of cellulose lose ester. The process presents substantial adacetate produced with the aid of sulphuric acid vantages o-ver prior processes in that the maas catalyst.

0 terial is not excessively reduced in particle size The stabilizing process may be effected in any during the treatment and thus does not contain suitable apparatus which is adapted to hold the a highpercentage of fines, i. e. extremely small cellulose ester in a substantially stationary condiparticles of cellulose ester which are of little tion and to permit the passage of the stabilizing commercial value. medium through the cellulose ester. One form of The invention is of particular value in the apparatus suitable for carrying out the process 35 stabilization ofcellulose acetate but may also consists essentially of a vessel provided with a be applied to the stabilization of other esters of false bottom near to the true bottom. The false cellulose, for example cellulose formate, cellubottom consists of a perforated plate and the lose propionate, and cellulose butyrate. Alcellulose ester to be stabilized is supported on this though the process of the invention is of special plate. Stabilizing liquor may be introduced into 40 value in the stabilization of esters which have and withdrawn from the vessel in any suitable been produced with the, aid of sulphuric acid as way, e. g. introduced by an inlet situated at the catalyst, it. is also of value in. the stabilization top of the vessel near to one side, and withdrawn of esters which have been produced in the presfrom an outlet situated at the bottom of the vessel ence of other catalysts, such as diand polybasic near to the other side, or the stabilizing liquor 45 acids and their derivatives, e. g. phosphoric acid, may be introduced into the top of the vessel sulphuryl chloride and sodium bisulphate. Celthrough a distributing device so as to be unilulose esters produced with the aid, as catalysts, formly applied to thesurface of the cellulose of metal halides or metal halides mixed with hyester, and withdrawn through an outlet at the drohalide acids, e. g. zinc chloride or ferric chlobottom of the Vessel. The inlet and outlet pipes 50 ride alone or mixed with hydrochloric acid, or for the stabilizing liquid are connected together produced with the aid, as catalysts, of perchloand include in their circuit a steam injector, ric acid and/or perchlorates e. g. zinc and magpump or other device adapted to maintain circunesium perchlorates, may also be treated by the lation of the stabilizing liquid through the vessel. 7

process of this invention. The bottom of the vessel may be provided with 5 jets for the introduction of steam into the vessel to keep the liquid contents of the vessel boiling.

It will be appreciated that this apparatus is susceptible of much variation and modification. Thus there may be more than one perforated plate carrying the cellulose ester, or the cellulose ester may be contained between two perforated plates so adjusted in relation to one another as to prevent any substantial movement of the cellulose ester which might arise from the boiling action of the liquid. Again, means may be provided to collect any cellulose esterwhich passes through the perforations in the plate or plates, and the outlet for the stabilizing liquid may be provided with a fine mesh gauze filter to prevent particles of cellulose ester from being carried to the circulating pump, if such is used. Preferably the stabilizationof the cellulose ester is effected at substantially atmospheric pressure though, if desired, the stabilization may be effected at superatmospheric pressures.

The stabilizing liquid is passed through the vessel until a test sample of the cellulose ester shows that its content of catalyst has been reduced to the desired degree. When stabilization is completed the cellulose ester may, if desired, be removed from the stabilizing vessel and subsequently washed and dried, or, as an alternative, these latter operations may be efiected in the stabilizing vessel itself. Thus the stabilizing liquid may be run off from the vessel and hot or cold water passed through the vessel to wash the "cellulose ester. After such washing operation the wash liquor may be drained off from the stabilizing vessel and then a warm gas such as dry steam or dry steam mixed with hot air may be forced through the vessel so as to dry the cellulose ester contained therein. It will thus be appreciated that by the process of the present invention the three steps of stabilizing, washing and drying may be carried out without any movement of the cellulose ester from one place to another.

The following example illustrates the invention, but is not to be taken as limiting it in any way.

Example Cellulose acetate is prepared with the aid of sulphuric acid as catalyst, ripened until it attains the desired solubility characteristics, and precipitated from the ripening solution. The precipitated cellulose acetate is then placed on a perforated false bottom in a suitable vessel and hot water is circulated through the vessel, thus washing the quiescent cellulose acetate. A 0.2% aqueous solution of sulphuric acid is then circulated through the vessel, the liquid in the vessel beingkept boiling by introducing steam into the vessel through jets situated in the true bottom of the vessel. The circulation of the aqueous sulphuric acid is continued until the stabilization of the cellulose acetate has proceeded to the desired degree. The aqueous sulphuric acid is then drained from the Vessel and the cellulose acetate washed by circulating water through the vessel. The cellulose acetate is then dried by draining 01f the liquid and passing hot air through the vessel.

By the process of this invention the stabilization of cellulose esters may be effected substantially without loss of material, e. g. in the form of fines, and the cellulose esters produced passes valuable properties in having a high heat test and in yielding artificial products of high clarity and uniformity. The esters are particularly valuable in the production of artificial filaments, threads, yarns, films, foils and the like by wet or dry spinning processes.

Having described my invention, what I desire to secure by Letters Patent is:-

1. Process for the stabilization of solid cellulose acetate which has been prepared in the presence of sulphuric acid as catalyst, which comprises stabilizing such cellulose acetate by passing a hot 0.01 to 0.03% aqueous solution of sulphuric acid continuously through the solid cellulose acetate While maintaining the cellulose acetate in a substantially stationary state.

2. Process for the stabilization of solid cellulose acetate produced in solution by esterifying cellulose with acetic anhydride in the presence of sulphuric acid as catalyst and precipitated from solution, which comprises stabilizing the solid, precipitated cellulose acetate by passing a hot 0.01 to 0.03% aqueous solution of sulphuric acid continuously through such cellulose acetate while maintaining such cellulose acetate in a substantially stationary state.

3. Process for the stabilization of solid cellulose acetate, which comprises stabilizing cellulose acetate by passing a hot 0.01 to 0.03% aqueous solution of sulphuric acid continuously through the solid cellulose acetate while maintaining the cellulose acetate in a. substantially stationary state.

4.. Process for the stabilization of solid cellulose acetate, which comprises stabilizing cellulose acetate by passing a hot 0.01 to 0.03% aqueous solution of sulphuric acid continuously through the solid cellulose acetate while maintaining the cellulose acetate in a substantially stationary state and under substantially atmospheric pressure.

5. Process for the stabilization of solid cellulose acetate, which comprises stabilizing cellulose acetate by passing a hot 0.01 to 0.03% aqueous solution of sulphuric acid continuously through the solid cellulose acetate while maintaining the cellulose acetate in a substantially stationary state and thereafter washing and drying the cellulose acetate while still maintaining it in a substantially stationary state.

JOHN EDWARD JONES. 

